The chicken anemia virus (CAV) causes infectious anemia in chickens. While CAV apparently can infect birds of all ages, signs of illness only have been reported in young birds. CAV's are also immunosuppressive. In normal healthy birds the thymus is responsible for the production of T-cells in young birds, the bursa of Fabricius produces B-cells and the bone marrow produces white blood cells in addition to red blood cells. When chicks are infected with CAV, destruction of said cells mentioned above occurs. Depression, anemia and immunosuppression occur within 7-14 days. Especially, chicks up to several weeks of age display severe signs of anemia and immunosuppression. Mortality rates in naturally-infected chicken flocks are usually up to 30% and recovery of the survivors usually becomes complete by 24-32 days post-infection.
Secondary infections, especially viral and bacterial infections, are common and enhance the symptoms caused by CAV raising the mortality rates in these instances well over 30%. Older birds may become infected but do not develop disease, although sub-clinical signs are considered to be the cause of a decline of the performance of the chickens.
Serological evidence indicates that in over 90% of tested chicken breeder flocks circulating CAV antibodies are present one time or another and hence were infected with the virus. The ubiquitous nature of CAV has well been reported.